ICL 7.1: Eye & Retina Flashcards
what are the parts of the eye?
out side
1. cornea
- anterior chamber
- iris
- pupil
- lens
- retina
inner most
what is inside the anterior chamber of the eye?
aqueous humor
what is the fovea?
the part of the eye with the highest seeing acute
what is the macula?
the space between the superior and inferior retinal arcade (vasculature)
which muscles does CN 3 innervate?
- superior rectus
- inferior rectus
- medial rectus
- inferior oblique
- pupil sphincter (parasympathetic)
- levator palpebrae
which muscles does CN 4 innervate?
superior oblique
which muscles does CN 6 innervate?
lateral rectus
which nerve controls the afferent pathway involving the pupils?
CN 2 controls the pathway from your eyes TO your brain
so CN 2 is what brings the light information to the brain
which nerve controls the efferent pathway involving the pupils?
CN 3 controls the pathway from your brain TO the eye
so CN 3 is what controls the eye muscles to react to the light
is CN 3 responsible for pupillary constriction or dilation?
constriction
it innervates the pupil sphincter!
pupillary constriction is controlled by the parasympathetic nervous system
what is the pupillary reaction to light?
if you shine a light in the left eye and everything is normal then the left pupil will constrict because CN 2 sent the information to the brain and then the brain sent information back to the eye via CN 3 to constrict the pupil
the right pupil will also constrict because of the consensual response!
what is an afferent pupillary defect?
if both eyes have an afferent pupillary defect and you shine light on the left eye, it won’t constrict because CN 2 is broken! glaucoma is the most common thing to damage CN 2 –> the right eye won’t constrict either because the afferent pathway is broken so there won’t be consensual constricting!
however, if there is an APD in the left eye but your right eye is okay and you shine light in the right eye, the right pupil will constrict AND and the left pupil will also constrict due to consensual response because even though the left afferents are broken, it’s efferents still work!
what is anisocoria?
this means the the pupils are different sizes
if you have an APD only in one eye, you WON’T have anisicoria because your efferent fibers are still working so you will have a consensual response that will still cause the broken eye to constrict
however, a condition that can cause one pupil to be smaller than the other is Horner syndrome which knocks out the sympathetic system and allows for uncontrolled parasympathetic responses which constrict your pupils!
which nerves control each of the muscles of the eye?
CN 3 controls the superior rectus, medial rectus, inferior rectus and inferior oblique
CN 4 controls the superior oblique
CN 6 controls the lateral rectus
which muscles of the eye will be spared in a retrobulbar block?
if you inject anesthetic into the muscular cone, the superior oblique will be the only functional eye muscle because CN 4 is outside the annulus of zenn so your eye will deviate down and out
CN 2, 3 and 6 are inside the annulus of zenn and also the nasociliary nerve (V1) and ophthalmic artery
CN 4, the superior opthalmic vein, frontal nerve and lacrimal nerve are all outside the annulus of zenn but inside the superior orbital fissure
which nerve is effected if a patient is unable to open their eyelid?
CN 3
CN 3 controls the levator palpebrae which opens your eye!
the other muscle responsible for opening the eye is the tarsal muscle which is sympathetically controlled so it’s not related to a CN and only does a few mm of eyelid opening –> so people with Horner’s syndrome who have knocked out their sympathetic nervous system will just have a mild ptosis since that knocks out the tarsal muscle but the levator palpebrae still works which does the majority of eye opening
how does CN 4 exit the brain?
it exits DORSALLY from the brainstem and travels around to the front to the eyeball so it has the longest intracranial course and is really susceptible to trauma!
CN 4 decussates as it exits the brain stem
note: it is the only cranial nerve to exit dorsally
what does a left-sided trochlear nerve palsy look like?
CN 4 = trochlear nerve
if CN 4 is knocked out then the superior oblique is knocked out and the left inferior oblique would be unopposed
this means the eye will be pointed up and out
which disease famously affects the ophthalmic division of the trigeminal nerve?
herepes zoster can cause herepes zoster ophthalmicus!
it’s when herpes reemerges as shingles and effects the V1 division of the trigeminal nerve!
this could effect the eyeball because V1 has to do with corneal sensation so shingles could damage the cornea!
the patient will present with what looks like stains on the cornea which are actually inflammation’they’re caratic precipitates which are collections of inflammatory cells that have deposited on the cornea and signify intraoccqular inflammation that’s being caused by the herpes zoster infection!
also the pupil won’t be round which is also caused by the inflammation which has caused the iris to scar down to the lens!! if there’s enough scarring you can block the pathway of aqueous humor out of the eye through the angles and you can get glaucoma too
what is CN 6 palsy?
CN 6 = abducens nerve which controls the lateral rectus
So if CN 6 is knocked out, the lateral rectus isn’t working so the eyes wouldn’t be about to look outwards
For example, if the left CN 6 isn’t working, that means the left eye lateral rectus is effected and that eye could look to the right but when it tries to look to the left, it would just get stuck in the middle —> however, the right eye would be able to look to the left because it’s CN 6 is fine
What is the most common cause of isolated CN 6 palsy?
Microvascular ischemia
So like someone with diabetes, hypertension, high cholesterol, or smoking could all effect CN 6 because all these diseases eventually cause strokes and heart attacks because they’re damaging the blood vessels and compromising blood flow to your organs!
What are the motor nerves of CN 7?
Temporal Zygomatic Buccal Mandibular Cervical
“To Zanzibar By Motor Car”
How would a facial nerve palsy effect the eye?
CN 7 controls the orbicularis oris so you wouldn’t be able to close your eye! You should be worried about chronic dryness which could scar your cornea and cause vision loss
Also, what is often seen is Bell’s phenomenon. So in the eye that can’t close, you will notice that the eye is pointed up. When you normally close your eyes the eyes move up and it’s a protective phenomenon so a person with facial palsy may still have an intact Bell’s reflex even though they can’t close their right eye
What is the diagnosis for someone who can’t see the cars around them when they are driving?
So this person’s vision quality is totally fine but they can’t see peripherally = bitemporal hemianopsia
The reason the peripheral vision is effected is because usually a pituitary tumor is impinging on the nasal retinal fibers —> the left temporal visual field correlates to the left nasal retina which is being impinged on by the pituitary tumor which is why you can’t see peripherally but your central vision is fine! The temporal fibers stay on the same side and don’t cross over the optic chiasm so they aren’t affected
On a visual field exam, the person would have the peripheral halfs of their vision blacked out = “respecting the vertical midline” which is a classic presentation for this condition